AST FINAL Flashcards
the total # of stars in the observable universe. is….
the # of grains on all the earths braches
speed of light in km
300,000 km per second
how long does it take light to go from the moon to earth
1 second
how long does it take light to travel from the earth to the sun
8 minutes
Which of these layers of the Sun is coolest?
photosphere
layers of sun from out to in
corona, chromosphere, photosphere
At the center of the Sun, fusion converts hydrogen into
helium, energy, and neutrinos.
the (blank) is the layer of the sun between its core and convection zone
radiation zone
Based on its surface temperature of 5,800 K, what color are most of the photons that leave the Sun’s surface?
green
Sunspots are cooler than the surrounding solar surface because
strong magnetic fields slow convection and prevent hot plasma from entering the region
What is granulation in the Sun?
the bubbling pattern on the photosphere produced by the underlying convection
What observations characterize solar maximum?
we see many sunspots
true or false, the corona brightens in x rays during a solar maximum
true
heliosphere
a bubble of solar wind which separates our planetary system from interstellar space
A main-sequence star twice as massive as the Sun would last __________.
half as long as the Sun
What happens to a low-mass star after helium flash?
Its luminosity goes down.
which of the following stars is most massive. AGM
A
AFK Which of these stars has the coolest surface temperature?
K
where on the HR diagram are cool and dim stars
bottom right
where on the HR diagram are hot and luminous stars
upper left
Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________.
cooler and larger in radius
Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________.
hotter and smaller in radius
What would happen to a neutron star with an accretion disk orbiting in a direction opposite to the neutron star’s spin?
its spin would slow down
A teaspoonful of white dwarf material on Earth would weigh
a few tons
what in size is closest to a white dwarf
the sun
true or false, Our Sun will probably undergo at least one nova when it becomes a white dwarf about 5 billion years from now
false
What kind of pressure supports a white dwarf?
electron degeneracy pressure
What is the upper limit to the mass of a white dwarf?
1.4 m sun
After a massive-star supernova, what is left behind?
either a neutron star or a black hole
What is the upper limit to the mass of a neutron star?
between 2 and 3 m sun
A teaspoonful of neutron star material on Earth would weigh
more than mt everest
Which of the following is closest in size (radius) to a neutron star?
a city
what would happen if a neutron star hit earth
earth would create a 1 cm film over it
From a theoretical standpoint, what is a pulsar?
a rapidly rotating neutron star
If you were to come back to our Solar System in 6 billion years, what might you expect to find of the sun?
a white dwarf
What does the famous formula have to do with special relativity?
It is a direct consequence of the theory, and hence a way of testing the theory’s validity.
true or false. Suppose that, as you sit in your classroom, you see two balls fall to the floor and hit at exactly the same time. According to the theory of relativity, other people sitting in the classroom with you will not agree that the balls hit the floor at the same time.
false
true or false? Different observers always agree about the order of events that occur at the same place.
true
true or false, the general theory of relativity deals with the effects of gravity, but the special theory of relativity does not take gravity into account.
true
The equivalence principle tells us that effects of these two things are indistinguishable:
gravity and acceleration
You know that you are following the straightest possible path through spacetime if
u r weightless
Why do we think that gravitational waves really exist?
We have observed orbiting objects that are losing precisely the amount of energy we expect them to be losing to gravitational waves.
Why do we see a gravitational redshift in the spectrum of the Sun?
Time runs slower on the Sun than on Earth, making lines in the solar spectrum have lower frequency and hence longer wavelength than normal.
Where are most of the Milky Way’s globular clusters found?
in the halo
Which of these forms of radiation passes most easily through the disk of the Milky Way?
infrared light
How does the diameter of the disk of Milky Way Galaxy compare to its thickness?
The diameter is about 100 times as great as the thickness.
the diameter of the milky way is?
100,000 light years
The Sun’s location in the Milky Way Galaxy is _________.
in the galactic disk, roughly halfway between the center and the outer edge of the disk
What do we mean by the interstellar medium?
the gas and dust that lies in between the stars in the Milky Way galaxy
What are the Magellanic Clouds?
two small galaxies that probably orbit the Milky Way Galaxy
How do disk stars orbit the center of the galaxy?
They all orbit in roughly the same plane and in the same direction.
What do we mean by the star-gas-star cycle?
It describes the orbits of the stars and interstellar medium around the center of the galaxy.
What are cosmic rays?
subatomic particles that travel close the speed of light
Which of the following analogies best describes how the structure of the galaxy’s spiral arms is maintained?
Like cars slowing in traffic to look at an accident, stars slow as they pass through the spiral arms.
What do we mean by a protogalactic cloud?
a cloud of hydrogen and helium that contracts to become a galaxy
Most stars in the Milky Way’s halo are young or old
old
What is an ionization nebula?
a colorful cloud of gas that glows because it is heated by light from nearby hot stars
In which of these galaxies would you be least likely to find an ionization nebula?
a large elliptical galaxy
true or false. Stars are continually forming in the halo of our Galaxy today.
false
true or false Spiral galaxies have more gas, dust, and younger stars than elliptical galaxies do.
true
A collision between two large spiral galaxies is likely to produce
an elliptical galaxy
The luminosity of a quasar is generated in a region the size of
the solar system
The primary source of a quasar’s energy is
gravitational potential energy.
Suppose a galaxy forms from a protogalactic cloud with a lot of angular momentum. Assuming its type has not changed due to other interactions, we’d expect this galaxy to be ______.
a spiral galaxy
Two ways in which the starting conditions in a protogalactic cloud might cause it to become an elliptical (rather than spiral) galaxy are if the cloud begins with either:
relatively little angular momentum or relatively high density
If the Andromeda Galaxy collided with the Milky Way, what would most likely happen to Earth?
nothing
Why do nearly all astronomers now agree that quasars really are quite far away?
We now have images and spectra that show quasars to be embedded at the centers of distant galaxies and within distant galaxy clusters.
Suppose we observe a source of X rays that varies substantially in brightness over a period of a few days. What can we conclude?
The X-ray source is no more than a few light-days in diameter.
Central black holes can be very efficient for converting the mass-energy of infalling matter to thermal energy in the accretion disk. Roughly what percentage of the mass-energy can be converted to other forms of energy as matter falls into a black hole?
10-40%
Why is a dense cloud more likely to produce an elliptical galaxy than a spiral galaxy?
The higher gas density forms stars more efficiently, so all the gas is converted into stars before a disk can form.
Which of these binary systems is most likely to contain a black hole?
an X-ray binary containing an star and another object of equal mass
How would a flashing red light appear as it fell into a black hole?
Its flashes would shift to the infrared part of the spectrum.
Where would be the most likely place to find an ionization nebula?
in a spiral arm
If you were to take a voyage across the Milky Way, what kind of material would you spend most of your time in?
warm, rarefied clouds of atomic hydrogen
Approximately how far is the Sun from the center of the galaxy?
28,000 lightyears
What is the galactic fountain model?
the theory that hot, ionized gas blown out of the galactic disk and into the halo by superbubbles cools down and falls back into the disk
Which of these colors of light passes most easily through interstellar clouds?
yellow
Astronomers estimate that new stars form in our galaxy at the rate of about
a few (2-3) a year
What is interstellar reddening?
Interstellar dust absorbs more blue light than red light, making stars appear redder than their true color.
What happens within a contracting cloud in which gravity is stronger than pressure and temperature remains constant?
It breaks into smaller fragments.
Which kind of object is the best standard candle for measuring distances to extremely distant galaxies?
a white dwarf supernova
When the ultraviolet light from hot stars in very distant galaxies finally reaches us, it arrives at Earth in the form of
visible light
The flat part of the Milky Way Galaxy’s rotation curve tells us that stars in the outskirts of the galaxy
orbit the galactic center just as fast as stars closer to the center.
Based on current evidence, which of the following is considered a likely candidate for the majority of the dark matter in galaxies?
subatomic particles that we have not yet detected in particle physics experiments
What kinds of atomic nuclei formed during the era of nucleosynthesis?
hydrogen and helium and trace amounts of lithium, beryllium, and boron
Approximately how long did the era of nucleosynthesis last?
3 minutes
Why does the Big Bang theory predict that the cosmic background radiation should have a perfect thermal radiation spectrum?
The background radiation came from the heat of the universe, with a peak corresponding to the temperature of the universe.
What are the two key observational facts that led to widespread acceptance of the Big Bang model?
the cosmic background radiation and the high helium content of the universe
Olbers’ paradox is an apparently simple question, but its resolution suggests that the universe is finite in age. What is the question?
Why is the sky dark at night?
In the 1960s, Maarten Schmidt determined that quasars were very distant objects by
determining their redshifts.
true or false. Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time.
false
How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced?
by gravity, which converts potential energy of matter falling toward a central black hole into kinetic energy, which is then converted to thermal energy by collisions among the particles of matter
If we represent the Milky Way Galaxy as the size of a grapefruit (10-cm diameter), the distance to the Andromeda Galaxy would be about
3m
galaxy
a great island of stars in space
light year
9.56 trillion km
planet
a moderetely sized object that orbits a star and shines primarely by reflecting light from that star. it must 1) orbit a star 2)large enough for its own gravity to make it round 3) has cleared most other objects from its orbital path
solar system
a star and all the things that orbit it
if you put all of history into one year, when were the pyramids built
11 seconds ago
from above what direction does the earth rotate
counterclockwise
how fast is the earth spinning
1,000 km per hour
how fast does the earth orbit the sun
100,000 km per hour
what is the earths axis tilt
23 degrees
how long does a galactic rotation take
230 million years
copernicus
polish scientist who applied calculatoins to aristarchus’s sun centered theory and knew it was correct. said it worked with weird circles…
Tycho Brahe
he used naked eye measurements to prove that supernovas were much farther away than the moon. he produced good data. but he thought that the sun orbited the earth while the other planets orbit the sun
kepler
hired by tycho. he came to the conclusion that orbits are elliptical
keplers 1st law
the orbit of each planet around the sun is an ellipse. planets are closer at perihelion and further at aphelion
keplers 2nd law
as a planet moves around its orbit, it sweeps out equal areas in equal time. therefore, planets move a greater distance when it is near perihelion than it does in the same amount near aphelion. faster when closer to the sun
perihelion
when a planet is closer to the sun
aphelion
when a planet is further from the sun
keplers 3rd law
- more distant planets orbit the sun slower.
- P^2=a^3. p is the orbital distance and a is the average distance
- thought magnetism (not gravity) kept planets orbiting the sun
hallmarks of science
seeks to explain observed phenomenon that rely on solely natural causes 2) science progresses through the creation and testing of models in nature that explain the obersvations as simply as possible 3) a scientific model must make testable predictions about natural phenomenon that will force us to revise or abandon the model if the predictions do not agree with the observations
occam’s razor
when a scientist chooses a simpler of 2 models that both work
theory
a model/generalization that stands up to testing again and again. cannot be proven beyond a doubt
conservation of momentum
the total momentum of interacting objects cannot change as long as no external force is acting on them. momentum is conserved
conservation of angular momentum
as long as there is no external torque (twisting force) the total momentum of a set of interacting objects cannot be changed
kinetic energy
energy of motion
radiative energy
energy carried by light
potential energy
stored energy, might be used as kinetic or radiative energy
thermal energy
the collective kinetic energy of many particles
mass energy
energy stored in mass
newton’s law of gravity
1) every mass attracts every other mass through gravity
2) the strength of the gravitational force attracting any 2 objects is directly proportional to the products of their masses
3) the strength of gravity between 2 objects decreases with the square of the distance between their centes (inverse square law)
doubling the distance between 2 objects weakens the gravitational force by
2^2=4
orbiting energy
the sum of an orbiting objects kinetic and gravitational energy. this total energy does not change even though one or the other can. balance is kept
earths escape velocity
40,000 km/hr 11 km/s
power
the rate of energy flow measured in watts
wavelength
the distance from one peak to the next
frequency
the number of peaks that pass through a point in a second
photons
the particles of light
is light a particle or a wave
both
atomic number
the number of protons
atomic mass number
the number of protons plus neutrons
isotope
an atom with a different number of protons
the only thing that affects a spectrum is
temperature
hot object= what frequency and wavelength
high frequency, short wavelength
doppler effect
when the spectra of light relative to us changes due to its motion
blue shift
coming toward us. wavelength shorter
redshift
moving away from us. wavelength gets longer
gravitational contradiction
the false theory from the 1800s that says the sun generates energy by slowly shrinking
corona
outermost level of the sun’s atmosphere that extends several million km above the sun. million k temp. X rays
chromosphere
middle layer of the suns atmosphere. and the region that radiates the suns UV temp of 10,000
photosphere
te lowest layer of the suns atmosphere. consists of a gas far less dense than the earths with a temperature of 6,000 k. visible light
convection zone
. just below atmosphere. where energy generated in the core travels upward, transportated by the rising of hot and cool gas
radiation zone
where energy moves outward primarily in the form of photons of light. Temp of 10 million k. is right outside the core. lots of x rays
core
temp of 15 k. fusion happens here
proton-proton chain
fusion process in low mass stars. 4 h–> 1 he + neutrino
what is happening to the brightness of the sun over time
generally increasing
what causes sunspots
magnetic fields poking out
solar flares
a storm that sends out charged particles of x rays and fast moving particles out into space.
sunspot cycle
a cycle in which the average number of sunspots on the sun gradually increases and falls. 11 years to go back from where it started from. whole cycle really 22 years
if the sun were viewed from 10 times the earths distance, it would be dimmer by a factor of what
10^10=100 if it were twice the distance it would be 2^2=4
which spectral type is the hottest and bluest OBAFGKM
O
which is hotter G1 or G9
G1
visual binary
a pair of stars that we can view orbiting eachother
eclipsing binary
a pair of stars that orbit in the plane of our sight. when neither star is eclipsed, we can see noth stars. when one is eclipsing the other, the brightness of the system drops
spectroscopic binary
a binary that is neither visual or eclipsing another one, we may detect it through doppler shifts or through spectral lines
power
the amount of energy emitted per second
true or false, The energy levels for electrons vary from one element to another.
true
What is the meaning of the wordcosmos
the sum total of all matter and energy, that is, everything within and between all galaxies
a light year is how many km
9.46 trillion
true or false, A star with spectral type F2 is hotter than a star with spectral type F3.
true
On a Hertzsprung-Russell diagram, where would we find stars that are cool and luminous?
upper righ
which side of the HR diagram is cooler
the right side
agol paradox
binary system when the less massive star gets mass from the larger one
what keeps a white dwarf from collapsing
electron degeneracy pressure
what happens to a red watch as it falls into a black hole
Eventually It becomes infrared than radio. The clock stops.
gamma ray bursts
• Some might come from powerful supernova explosions (the kind that creates black holes)
what are the 2 ways that stars return gas to the universe through galactic recycling
stellar winds or supernova. this process returns gas but also changes the % of heavy elements
disk population
contains both young and old stars, all of which have heavy element proportions of about 2%, like our sun
spheroidal population
consists of stars in the halo and the bulge, both of which are roughly spherical in shape. Stars in this population are always old and therefore low in mass, and those in the halo sometimes have heavy element proportions as low as .02%
what is the minimum mass of a star and why does it exist
.08 and because their central temperatures never climb above 10 million k needed for fussion • Degeneracy pressure, which depends on the mass of an object, halts gravitational contraction before hydrogen burning can begin
brown dwarf
• The result of a protostar with a mass of .08 and degeneracy pressure is a failed star, that slowly radiates away its thermal energy
